1. Field of the Invention
The present invention relates to an image reading device and a vertical stripe determination method.
2. Description of the Related Art
In an image reading device, what is called sheet-through reading is performed during which an original is carried in the sub-scanning direction while keeping a reading unit fixed, and image reading is performed on the surface of a reading glass. During sheet-through reading, if any dirt is present on the reading glass (surface), a defective image having vertical stripes (unintended lines continuous in the sub-scanning direction) gets generated.
In order to prevent generation of such a defective image, various proposals have been put forward in the past. For example, prior to performing a reading operation, it is determined whether any foreign particle is present on an optical component, such as carrying rollers or a belt, other than the reading glass (hereinafter, simply referred to as “components except the reading glass”) or on the reading glass (surface). Besides, in case vertical stripes are formed, it is also known that image processing is performed with the aim of correcting the vertical stripes or that automatic cleaning of the reading glass is carried out.
In such conventional technologies, the dirt present on the reading glass (surface) is detected using a carried original. For that reason, even if the dirt is detected, the carried original used for dirt detection needs to be reprinted, which requires time and effort of the user. In addition to that, in the conventional dirt detection technique, it is nothing more than simply providing information about whether the dirt is present on the reading glass or on the components except the reading glass. That is, no determination of the cause of the vertical stripes is performed, and no appropriate measures for preventing formation of the vertical stripes are notified to the user. Hence, such information is not sufficient in order to perform vertical stripe correction. Moreover, even if vertical stripes are detected and if an operation of correcting vertical stripe images is performed, it may lead to a decline in the image quality. Furthermore, as far as the vertical stripes caused due to a scratch on the reading glass is concerned, neither automatic cleaning of the reading glass enables achieving the fundamental solution, nor it is possible to determine such a cause.
For such reasons, the conventional technology fails to be adequate in determining the cause of the generation of vertical stripe images. Besides, if correction of vertical stripe images is performed, it may have an impact on the image quality.
For example, in Japan Patent Application Laid-open No. 2001-272829 is disclosed a technology in which reading is done by moving an original while keeping the optical system fixed (sheet-through reading). During such reading, it is determined whether any foreign particle is present on a white board (a pressurizing board) or on a contact glass of an automatic original carrying unit. Thus, in Japan Patent Application Laid-open No. 2001-272829, there is description about the means for moving the contact glass in either the same direction as an original or in an orthogonal direction to an original and about the means for detecting the dirt. As far as the means for detecting the dirt is concerned, a foreign particle detecting circuit compares a read image obtained before the contact glass is moved with a read image obtained after the contact glass has been moved, and determines whether any dirt is present on the white board (the pressurizing board) or on the contact glass of the automatic original carrying unit.
Such a conventional device is similar to the present invention described below on the issue of determining the location (whereabouts) of causing vertical stripe images during sheet-through reading. However, after the location causing the vertical stripe images is determined (i.e., after a causing matter (described later) is determined), it is not possible to determine the type of that causing matter. Besides, no means is available for notifying the appropriate measures to be taken against that cause. Moreover, since it is not possible to distinguish between the dirt present on the reading glass and a scratch on the reading glass, the issue that the user does not have adequate information for removing vertical stripe images remains unresolved.
Therefore, there is a need for an image reading device that capable of providing if vertical stripes are formed in a read image, not only location information regarding the causing matter of vertical stripes but information regarding the type of the causing matter.